Add NoSourceLocationMarker in old source-info engine.

tests/compiler/dart2js/sourcemaps/sourcemap_helper.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library sourcemap.helper;
 
 import 'dart:async';
 import 'dart:io';
 import 'package:compiler/compiler_new.dart';
 import 'package:compiler/src/apiimpl.dart' as api;
@@ skipping 120 matching lines @@
 
   @override
   void register(js.Node node, int codeOffset, SourceLocation sourceLocation) {
     nodeToSourceLocationsMap.register(node, codeOffset, sourceLocation);
     sourceMapper.register(node, codeOffset, sourceLocation);
   }
 }
 
 /// A wrapper of [SourceInformationProcessor] that records source locations and
 /// code positions.
-class RecordingSourceInformationProcessor
-    implements SourceInformationProcessor {
+class RecordingSourceInformationProcessor extends SourceInformationProcessor {
   final RecordingSourceInformationStrategy wrapper;
   final SourceInformationProcessor processor;
   final CodePositionRecorder codePositions;
   final LocationMap nodeToSourceLocationsMap;
 
   RecordingSourceInformationProcessor(this.wrapper, this.processor,
       this.codePositions, this.nodeToSourceLocationsMap);
 
   @override
   void onPositions(
@@ skipping 398 matching lines @@
       absoluteUri = base.resolveUri(uri);
     } else {
       absoluteUri = base.resolve(uri);
     }
     return sourceFiles.putIfAbsent(absoluteUri, () {
       String text = new File.fromUri(absoluteUri).readAsStringSync();
       return new StringSourceFile.fromUri(absoluteUri, text);
     });
   }
 }